1. Field
The present invention relates to an organic light emitting display (OLED).
2. Related Art
In general, an organic light emitting display is a self-emitting display for emitting light by electrically exciting a fluorescent compound and has been spotlighted as a future generation display that can solve problems of a liquid crystal display as it can be driven in a low voltage, easily reduce a thickness, have a wide viewing angle and a fast response speed, etc.
The organic light emitting display comprises an organic emitting layer between an anode and a cathode. The organic light emitting display forms an exciton, which is a hole-electron pair, by coupling a hole received from the anode and an electron received from the cathode within the organic light emitting layer and emits light by generating energy when the exciton returns to a ground level. The organic light emitting display further comprises a hole (electron) injecting layer and/or a hole (electron) transporting layer between the anode or the cathode and the emitting layer.
Depending on a driving mode, an OLED is usually classified into a passive matrix organic light emitting display (PMOLED) and an active matrix organic light emitting display (AMOLED).
FIG. 1 illustrates a conventional OLED 100.
Referring FIG. 1, a driving unit 130 is formed over a substrate 100 and a planarization layer 150 is formed on the driving unit.
The driving unit 130 comprises at least a thin film transistor for driving. The thin film transistor comprises a gate electrode 131, a gate insulation layer 132, an active layer 133 made of amorphous silicon, an ohmic contact layer 134, a source electrode 135 and a drain electrode 136.
An emission unit 140 is formed on the planarization layer 150 to be connected to the driving unit 130. The emission unit 140 comprises a first electrode 141 connected to the drain electrode 136, an organic emitting layer 143 and a second electrode 144.
An insulating layer 142 is formed on the first electrode 141 exposing a portion of the first electrode 141. The organic emitting layer 143 is formed on the exposed portion of the first electrode 141.
A passivation layer 160 is formed on the emission unit 140 to cover the emission unit 140 and the planarization layer 150. A cover substrate 120 is attached to the substrate 110 comprising the passivation layer 160. The substrate 110 and the cover substrate 120 are attached with a sealant 170.
Moisture and oxygen penetrating inside the OLED may damage the organic emitting layer and the electrodes. More specifically, moisture passes into a pin hole formed in a portion of a cathode or into an edge portion between the cathode and a barrier rib, and reacts with organic layer and the electrodes, thereby generating hydrogen.
Such hydrogen diffuses to the left and right sides on an interface between the cathode and the organic emitting layer, causing generation of bubbles over the organic emitting layer. As a result, an event in which the cathode is lifted up occurs frequently. Also, when oxygen transmits through the pin hole of the cathode or the edge portions between the cathode and a barrier rib, an oxide layer is likely to be formed on the cathode at the interface between the cathode and the organic emitting layer. This oxide layer often shields a flow of current.
In the above described conventional OLED 100, the passivation layer 160 is formed to protect the driving unit 130 and the emission unit 140. Particularly, an edge portion of the passivation layer 160 is formed to be inclined inwardly. In other words, the passivation layer comprises a normal tapered edge portion. However, since an edge portion of the planarization layer 150 are formed to have corners nearly perpendicular, the passivation layer 160 is not well deposited on the edge portions of the planarization layer 150. As a result, adhesion between the planarization layer 150 and the passivation layer generally becomes poor.
Accordingly, the driving unit 130 and the emission unit 140 may not be effectively protected by the passivation layer 160, because moisture and oxygen are more likely to penetrate into the devices from the outside through the passivation layer 160